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Regulatory Assets and Liabilities (Regulated Liabilities) (Details) - CAD ($) $ in Millions | Dec. 31, 2018 | Dec. 31, 2017
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Regulatory Liabilities [Line Items] |  |
Regulatory Liability, Current | $ 251 | $ 226
Regulatory Liability, Noncurrent | 2,359 | 2,242
Regulatory Liabilities, Total | 2,610 | 2,468
Deferred income tax regulatory assets [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory Liabilities, Total | 1,218 | 1,116
Accumulated reserve - cost of removal [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory Liabilities, Total | 955 | 894
Deferrals related to derivative instruments [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory Liabilities, Total | 116 | 182
Fuel Adjustment Mechanism Liability [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory Liabilities, Total | 161 | 177
Cost Recovery Clauses Liability [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory Liabilities, Total | 30 | 51
Self Insurance Fund [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory Liabilities, Total | 30 | 28
Storm Reserve [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory Liabilities, Total | 76 | 0
Other Regulatory Assets (Liabilities) [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory Liabilities, Total | $ 24 | $ 20

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- Definition The amount for the individual regulatory liability as itemized in a table of regulatory liabilities as of the end of the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 405 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6500807&loc=d3e48068-110394 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition The amount for the individual regulatory current liability as itemized in a table of regulatory current liabilities as of the end of the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 405 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6500807&loc=d3e48068-110394 + Details
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- Definition The amount for the individual regulatory noncurrent liability as itemized in a table of regulatory noncurrent liabilities as of the end of the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.24) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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